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  #1  
Old 28th January 2020, 11:05 PM
daxtojeiro daxtojeiro is offline
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Location: Norwich
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Default Pre Amp wire

Hi all.
I have a passive pre-amp that I built years ago. It's basically an ALPs pot, a selector switch and some quality phono cable. (screened)
Looking at it, its a mess inside and I'm thinking about re-wiring it. I have seen pictures using un-screened cable and what looks like resistors in line with the switches.

I've also grounded the chassis, connecting the input / output grounds via a 100R / 0.1uF capacitor in parallel.

Is this grounding method OK, or should I totally insulate it and only allow the grounds of the inputs / outputs to connect at the main amp?

Is there a good quality, but thin cable I should be using for the cabling inside, as my thick old cable with shielding has made it a bit of a mess inside.

I have seen selector switches with resistors on them, what are they used for, I have nothing on mine, its simply wires, switches and a pot,
thanks for your hep
Phil
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  #2  
Old 29th January 2020, 09:10 AM
snowman_al snowman_al is offline
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Location: West Wales
Posts: 63
Default Re: Pre Amp wire

Quote:
Originally Posted by daxtojeiro View Post
Hi all.
I have a passive pre-amp that I built years ago. It's basically an ALPs pot, a selector switch and some quality phono cable. (screened)
Looking at it, its a mess inside and I'm thinking about re-wiring it. I have seen pictures using un-screened cable and what looks like resistors in line with the switches.

I've also grounded the chassis, connecting the input / output grounds via a 100R / 0.1uF capacitor in parallel.

Is this grounding method OK, or should I totally insulate it and only allow the grounds of the inputs / outputs to connect at the main amp?

Is there a good quality, but thin cable I should be using for the cabling inside, as my thick old cable with shielding has made it a bit of a mess inside.

I have seen selector switches with resistors on them, what are they used for, I have nothing on mine, its simply wires, switches and a pot,
thanks for your hep
Phil
The switch with resistors on is likely to be a 'stepped attenuator' or stepped volume control. Basically the alps pot, but with 23 or 41 or so positions instead of the constant variable track of the pot. It can give better channel balance as the resistors can be matched accurately. Posh one use posh types of resistor too...

Thin wire ummm. CAT5 or 6 network cable stripped and made into twisted pairs is fine and well liked. All the way to silver wire and Teflon insulation. Like the stepped control, price is the only constraint!

If the enclosure is metal best to have it earthed to mains earth, just in case.
Ground lifting the signal ground (the 100R/0.1uF) is fine, it is to stop earth or ground loop mum.
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  #3  
Old 29th January 2020, 10:44 AM
A Stuart A Stuart is offline
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Location: Selkirk, Scotland
Posts: 284
Default Re: Pre Amp wire

... or else resistors were put in to compensate for different outputs from different sources?
... or the "shunt modification" in FAQs>Upgrades and tweaks. http://www.world-designs.co.uk/forum...ead.php?t=5795
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  #4  
Old 29th January 2020, 11:57 AM
Richard Richard is offline
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Location: Notts
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Default Re: Pre Amp wire

Yes I've done a few, with and without the shunt pot resistors, and use enamelled copper wire. I use isolated phonos, an ally box for overall screening, and earth the box and pot (for safety and to stop hums) to the phono screens.
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  #5  
Old 29th January 2020, 12:07 PM
Richard Richard is offline
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Default Re: Pre Amp wire

Here's one with shunt pot,
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  #6  
Old 29th January 2020, 12:32 PM
Ali Tait's Avatar
Ali Tait Ali Tait is offline
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Location: Leeds
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Default Re: Pre Amp wire

I think you'd get more bang for the buck swapping out the Alps for something better.
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  #7  
Old 29th January 2020, 01:56 PM
Chris Chris is offline
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Location: Peterborough
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Thumbs up Re: Pre Amp wire

Really nice work Richard..

Chris
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  #8  
Old 29th January 2020, 08:21 PM
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Greg. Greg. is offline
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Location: Bristol, UK
Posts: 3,389
Default Re: Pre Amp wire

Quote:
Originally Posted by Ali Tait View Post
I think you'd get more bang for the buck swapping out the Alps for something better.
Maybe Ali, but I suspect when used with the shunt pot mod, it makes little difference because the wiper is not passing signal.
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